Optical transmitter

ABSTRACT

The present invention provides an optical transmitter for transmitting an optical signal using an optical fiber as a transmission medium. The optical transmitter comprises: a substrate having a through hole; and a light-emitting element disposed on a rear surface of the substrate and having a light-emitting portion. The through hole has an inner wall. The through hole has an inside diameter increasing from a rear surface side of the substrate toward a front surface side thereof. The light-emitting element is disposed so that the light-emitting portion is exposed within the through hole. The light-emitting portion radiates light beams toward a front surface of the substrate. The through hole is such that part of the light beams goes out the through hole without being reflected, and that the other light beams go out the through hole after being reflected from the inner wall thereof. It is possible to increase the coupling efficiency of the optical transmitter by effectively utilizing a light beam light having a wide radiation angle, and improve heat dissipation thereof, while achieving miniaturization and cost reduction of the optical transmitter.

TECHNICAL FIELD

The present invention relates to an optical transmitter. Moreparticularly, the present invention relates to an optical transmitterfor transmitting an optical signal using an optical fiber as atransmission medium.

BACKGROUND ART

There have been known optical transmitters using a light-emitting diodeas a light source and a multimode optical-fiber as a transmission mediumin domestic communications, in communications inside of motor vehiclesand the like using LAN (Local Area Network). As prior arts associatedwith the present invention, the following are known.

(1) A photosemiconductor device characterized by comprising: a pair ofconductive leads arranged facing each other; a metal container having areflecting surface and disposed at a distal end of one of the conductiveleads; a photosemiconductor element disposed on the reflecting surfaceof the metal container, one electrode of the photosemiconductor elementbeing connected to one of the conductive leads; and a wire forconnecting the other electrode of the photosemiconductor element to theother conductive lead (see, e.g., Japanese Unexamined Patent PublicationNo. Sho 58(1983)-56483).

(2) A light-emitting element for optical fiber coupling, which, via atransparent member, leads a light beam emitted from a light-emittingelement pellet disposed on a light-emitting element supporter, thelight-emitting element characterized by comprising the transparentmember having a flat disc-shaped central portion and a peripheralportion, the flat disc-shaped central portion facing the light-emittingelement pellet, the peripheral portion having a thickness decreasing asthe distance from the center of the transparent member increases (see,e.g., Japanese Unexamined Patent Publication No. Sho 59(1984)-180515).

(3) A semiconductor light-emitting device characterized by comprising: acase; a light-emitting element accommodated in the case; lead membersfor supplying electric power to the light-emitting element from theoutside; a connecting portion defined on the case for connecting anoptical fiber to the case, the optical fiber guiding a light beamemitted from the light-emitting element so that the light beam isradiated via the optical fiber connected to the connecting portion; anda concave reflecting surface facing a light-emitting surface of thelight-emitting element for reflecting the light beam emitted from thelight-emitting element and thereby directing the light beam to alight-receiving surface of the optical fiber (see, e.g., JapaneseUnexamined Patent Publication No. Hei 1(1989)-241185).

(4) A range finder measuring distances to a plurality of points,characterized by comprising a plurality of light-emitting sources and atleast one photoreceptor, the light-emitting source being semiconductorchips respectively mounted on the bottoms of a plurality of recessesformed in a lead frame (see, e.g., Japanese Unexamined PatentPublication No. Hei 3(1991)-188312).

(5) A projector characterized by comprising (i) a half or less than ahalf of a paraboloid of revolution obtained by dividing a paraboloid ofrevolution by a face containing the axis of revolution, the half or lessthan half having a specular surface in the form of a paraboloid, and(ii) a light source arranged near a focal point on the paraboloid sothat a center luminous flux of light emitted from the light source isincident on the specular surface (see, e.g., Japanese Unexamined PatentPublication No. Sho 62(1987)-17721).

(6) An optical coupling device for guiding, to a light-receiving surfaceat a proximal end of an optical fiber, a light beam emitted from alight-emitting element, the optical fiber being arranged facing thelight-emitting element, the optical coupling device characterized bycomprising: a transmissive-type light-collecting means arranged betweenthe light-emitting element and the optical fiber for allowing a lightbeam emitted from the light-emitting element to pass through thetransmissive-type light-collecting means so that the light beam iscollected onto the optical fiber; and a reflective-type light-collectingmeans arranged around the transmissive-type light-collecting means, thereflective-type light-collecting means having a reflecting surface forreflecting a light beam radiated from the light-emitting element so thatthe light beam is collected onto the optical fiber, the reflectingsurface of the reflective-type light-collecting means being a rotaryelliptical surface, the rotary elliptical surface forming two focalpoints, the light-emitting element being arrange on one of the focalpoint, the light-receiving surface of the optical fiber being arrangedon the other focal point (see, e.g., Japanese Unexamined PatentPublication No. 2002-40299).

(7) A structure for mounting a light-emitting diode comprising: a firstlead frame having a chip-mounting seat with a photo penetration holeformed though the chip-mounting seat; an LED chip mounted on the firstlead frame so that a light-emitting surface of the LED chip faces thephoto penetration hole of the first lead frame; and a second lead framebonded to a rear electrode of the LED chip by a wire, the structurecharacterized in that the LED chip, the wire, and distal ends of therespective first lead frame and second lead frame are covered with atransparent resin (see, e.g., Japanese Unexamined Patent Publication No.Sho 60(1985)-12782).

As a common optical transmitter for coupling an LED (light-emittingdiode) and an optical fiber, there is known, for example, an opticaltransmitter, shown in FIG. 21, which is produced by transfer mold.

The optical transmitter 101 shown in FIG. 21 comprises a lead frame 105,an LED 103 arranged on the lead frame 105, a mold resin 109 that coversthe lead frame 105 and the LED 103, a lens 104 formed of the same resinthat forms the mold resin 109, and an optical fiber 102. Light beamsradiated from the LED 103 are collected by means of the lens 104 ontothe optical fiber 102.

However, there is a problem with this optical transmitter that it isdifficult to couple light beams radiated form the LED 103 into theoptical fiber 102 with high efficiency.

This problem is associated with a far field pattern (FFP) of an LEDshown in FIG. 22. That is, the far field pattern of the LED is theLambert Pattern where generally, the radiation intensity of the LED isrepresented by the cosine function. The far field pattern of the LED hasa feature that a light beam from the LED has a wide radiation angle whencompared with one from a semiconductor laser or the like. For thisreason, in the optical system shown in FIG. 21, which is produced bytransfer mold, a light beam having a wide radiation angle, of lightbeams emitted from the LED 103, cannot be coupled to the lens 104,giving rise to a loss.

One approach to this problem is to bring the lens 104 closer to the LED103 for coupling a light beam having a wide radiation angle to the lens104. However, bringing the lens 104 closer to the LED 103 causes thefailure to ensure in a direction of the thickness of the opticaltransmitter a space required for wire-bonding of an electrode of the LED103 to the lead frame. Further, the above approach requires that thelens 104 has a reduced focal length (i.e., that the lens 104 has aflattened curvature). With all these things considered, it is difficultto take the approach of bringing the lens 104 closer to the LED 104 toincrease the efficiency of coupling in the optical fiber 102.

On the other hand, there have been proposed various methods of changingthe optical path of a light beam having a wide radiation angle byreflecting the light beam from a concave mirror to increase the utilityefficiency of light beams.

As a common optical transmitter utilizing a concave mirror, there isknown, for example, one shown in FIG. 23.

In an optical transmitter 201, shown in FIG. 23, a substrate 205 has aconcave portion in a part thereof. The concave portion serves as aconcave mirror 108 having high reflectance and having an inside diametergradually increasing from a bottom surface side thereof toward an upperedge side thereof. A LED 103 is disposed so that a rear surface side ofthe LED 103 (opposite a light-emitting surface 106) is in contact withthe bottom surface side of the concave portion.

Of light beams radiated from the light-emitting surface 106 of the LED103, a light beam having a wide radiation angle is reflected from theconcave mirror 108 so that its optical path is changed toward a distalend of an optical fiber, not illustrated. Thus, even a light beam havinga wide radiation angle can also be effectively used.

However, in an optical transmitter using a concave mirror, it isdifficult to increase the coupling efficiency while achievingminiaturization and cost reduction of the optical transmitter.

That is, for example, in the optical transmitter 201 shown in FIG. 23,assuming that: the LED 103 is in the shape of a cube with a height of300 μm and a width of 300 μm; the concave mirror 108 has a cone angle θof 60°; and the concave portion has an inside diameter of φ 500 μm onthe bottom surface side thereof, the concave portion needs to have adepth T0 of about 1.3 mm and an inside diameter R0 of 2 mm on the upperedge side in order for the concave mirror 108 to change the optical pathof a light beam having a radiation angle of 45° or wider, of light beamsradiated from the center of the light-emitting surface 106 of the LED103. As a result, a lens with a diameter of φ 2 mm or greater is neededto collect and then couple into the optical fiber the light beams theoptical paths of which have been changed by the concave mirror 108.

If the inside diameter of the concave mirror 108 on a side at whichradiated light beams are raised, i.e., on the upper edge side, is aslarge as about φ 2 mm, there is a risk that, when a lens with a shortfocal length is used to collect light beams, the light beams may not beable to be coupled into the optical fiber because an NA incident to theoptical fiber becomes so large that the light beams cannot be coupledinto the optical fiber. On the other hand, when using a lens with a longfocal length in order to take an advantage of a small incident NA, it isdifficult to miniaturize the optical transmitter inclusive of theoptical fiber.

Here, if the concave mirror 108 is curved, the optical transmitter canbe slightly miniaturized, but is still larger than the one shown in FIG.21. Further, a space needs to be provided at a portion of the concavemirror 108 for wire-bonding the electrode of the LED 103, whichcomplicates the production process and widens a variation intransmission efficiency and thus a variation in the quantity of lightcoupled into the optical fiber. That is, depending on precisions in thelocation and shape of the concave mirror 108, the direction of lightvaries to result in variation in transmission efficiency, which widens avariation in the quantity of light coupled into the optical fiber. Thiscreates the need to increase the dynamic range in optical transmission.Also, the substrate 205 needs to have therein the concave mirror 108,which results in a high cost. As has been explained above, in an opticaltransmitter using a concave mirror, after all, it is difficult toincrease the coupling efficiency while achieving miniaturization andcost reduction of the optical transmitter.

Other than optical transmitters having the concave mirror, there areknown one having a parabola-shaped mirror for improvement in couplingefficiency, one in which a mirror is provided on a side of a lens, andthe like. These optical transmitters are problematic in that the numberof components is increased to result in upsizing and a rise in the costof the optical transmitters.

On the other hand, there is known an optical transmitter having (i) alead frame with an opening formed therein and (ii) an LED having alight-emitting surface joined to the lead frame so that a light beamradiated from the light-emitting surface passes through the opening tobe coupled into an optical fiber. In such an optical transmitter havingthe LED arranged on a rear surface of the lead frame, wire-bonding ismade on the rear surface side opposite to the front surface side of thelead frame, i.e., to the side at a lens is provided. As a result, thelens (or the optical fiber) can be arranged close to the LED withoutconsidering a space required for the above-mentioned wire-bonding sothat a relatively high coupling efficiency can be obtained.

However, only forming the opening through the lead frame for a lightbeam to pass through the opening does not make it possible to guide alight beam with a wide radiation angle to the lens at an effectiveangle. Therefore, it is eventually difficult to utilize a light beamwith a wide radiation angle.

Meanwhile, in an optical transmitter, dissipation of heat generated in alight-emitting element is also important. If the optical transmitter ispoor in heat dissipation, the temperature of a light-emitting elementchip itself rises. Therefore, the magnitude of an electric currentallowed to pass through the light-emitting element is limited, and theenvironment in which optical transmitters can be used is limited to makeit impossible to use them in environments where the temperature is highsuch as motor vehicles and production facilities. For this reason, thereis a need to reduce a thermal resistance of the LED chip and membersaround the LED chip. As a method of reducing the thermal resistance,there is known a method by disposing the LED chip on a substrate of amaterial good in heat dissipation. However, with this method there is aproblem in that the thermal resistance of the LED chip itself cannot bereduced and that a high cost and upsized optical transmitters areresulted.

On the other hand, in the conventional optical transmitter 101 shown inFIG. 21, in which a surface of the LED 103 is covered with the moldresin 109, there is a problem in that a great thermal stress is createdon the LED 103 when the ambient temperature varies, due to a largedifference in a linear expansivity generally present between the LED 103and the mold resin 109. For example, GaAs generally used in a red LEDhas a linear expansivity of about 6 ppm/K, while the material of thetransparent mold resin such as an epoxy resin or the like has a linearexpansivity of 60 ppm/K to 65 ppm/K, values substantially an order ofmagnitude greater. For this reason, there is a problem in that, inenvironments where wide temperature variations (e.g., from −40° C. to110° C.) are encountered as expected in vehicle-installed devices andthe like, a great thermal stress is applied onto the light-emittingsurface of the LED 103 to make the light emission state unstable or makethe LED 103 broken, or a bonding wire is ruptured due to a difference inlinear expansivity between the bonding wire and the epoxy resin. Thus,it is difficult to gain a high reliability.

DISCLOSURE OF INVENTION

The present invention has been made under these circumstances, and it isan object of the present invention to provide an optical transmittergood in heat dissipation which has high coupling efficiency. The opticaltransmitter can also be miniaturized and manufactured at a low cost, andcan be used and stored over a wide temperature range.

The present invention provides a first optical transmitter comprising: asubstrate having a through hole; and a light-emitting element disposedon a rear surface of the substrate and having a light-emitting portion,the through hole having an inner wall, the through hole having an insidediameter increasing from a rear surface side of the substrate toward afront surface side thereof, the light-emitting element disposed so thatthe light-emitting portion is exposed within the through hole, thelight-emitting portion radiating light beams toward a front surface ofthe substrate, the through hole being such that part of the light beamsgoes out the through hole without being reflected, and that the otherlight beams go out the through hole after being reflected from the innerwall thereof.

In the first optical transmitter according to the present invention, thesubstrate has the through hole. The through hole has the inner wall. Thethrough hole has the inside diameter increasing from the rear surfaceside of the substrate toward the front surface side thereof. Thus, oflight beams radiated from the light-emitting portion, a light beamhaving a wide radiation angle can be reflected from the inner wall ofthe through hole toward the front surface of the substrate. Accordingly,the light beam having a wide radiation angle, of the light beamsradiated from the light-emitting element, can be also effectivelyutilized for optical coupling into an optical fiber or the like,increasing the coupling efficiency.

The light-emitting element is disposed on the rear surface of thesubstrate so that the light-emitting portion is exposed within thethrough hole. Thus, the light-emitting portion of the light-emittingelement is close to the inner wall of the through hole. Accordingly, itis possible to reduce to a minimum the depth of the through holeinvolved in reflection of a light beam having a wide radiation angletoward the front surface of the substrate. Consequently, miniaturizationof the optical transmitter can be achieved.

The through hole formed in the substrate serves as a guide for lightbeams radiated from the light-emitting element. Thus, the substrateoriginally for use as a wiring component can also be utilized as anoptical component. Accordingly, the number of components can be reducedand the production process can be simplified. Consequently, costreduction of the optical transmitter can be achieved.

The light-emitting element is disposed so that the light-emittingportion is exposed within the through hole. Thus, the light-emittingportion as a heat-generating source is close to the substrate as aheat-dissipating medium. Accordingly, heat dissipation of thelight-emitting element is improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a schematic construction of anoptical transmitter according to Embodiment 1 of the present invention;

FIG. 2 is a plan view of a light-emitting element used in the opticaltransmitter of FIG. 1;

FIG. 3 is a cross sectional view of the light-emitting element of FIG.2;

FIG. 4 is an enlarged view of an essential part of the opticaltransmitter 1 of FIG. 1;

FIG. 5 is an explanatory view in which the size of the opticaltransmitter 1 according to Embodiment 1 is compared with that of aconventional optical transmitter on the same figure;

FIG. 6 is a plan view of a through hole formed in a lead frame of theoptical transmitter of FIG. 1;

FIG. 7 is a cross sectional view of the through hole of FIG. 6;

FIG. 8 is a plan view showing a modification of the through hole;

FIG. 9 is a cross sectional view of the through hole of FIG. 8;

FIG. 10 is a plan view of another modification of the through hole;

FIG. 11 is a cross sectional view of the through hole of FIG. 10;

FIG. 12 is a plan view showing still another modification of the throughhole;

FIG. 13 is a cross sectional view of the through hole of FIG. 12;

FIG. 14 is an explanatory view showing a schematic construction of anoptical transmitter according to Embodiment 2 of the present invention;

FIG. 15 is an enlarged view of an essential part of an opticaltransmitter according to Embodiment 3 of the present invention;

FIG. 16 is an enlarged view of an essential part of an opticaltransmitter according to Embodiment 4 of the present invention;

FIG. 17 is a view showing in detail a rear surface side of a submount ofFIG. 16;

FIG. 18 is an explanatory view showing a schematic construction of anoptical transmitter according to Embodiment 5 of the present invention;

FIG. 19 is an explanatory view showing a schematic construction of anillumination device according to Embodiment 6 of the present invention;

FIG. 20 is an explanatory view showing a schematic construction of anillumination device according to Embodiment 7 of the present invention;

FIG. 21 is an explanatory view showing a schematic construction of aconventional optical transmitter;

FIG. 22 is an explanatory view showing an example of a far field patternof an LED; and

FIG. 23 is an explanatory view showing a schematic construction of theconventional optical transmitter.

BEST MODE FOR CARRYING OUT THE INVENTION

A first optical transmitter according to the present invention ischaracterized by comprising: a substrate having a through hole; and alight-emitting element disposed on a rear surface of the substrate andhaving a light-emitting portion, the through hole having an inner wall,the through hole having an inside diameter increasing from a rearsurface side of the substrate toward a front surface side thereof, thelight-emitting element disposed so that the light-emitting portion isexposed within the through hole, the light-emitting portion radiatinglight beams toward a front surface of the substrate, the through holebeing such that part of the light beams goes out the through holewithout being reflected, and that the other light beams go out thethrough hole after being reflected from the inner wall thereof.

In the present invention, the term “radiated light beam” refers to alight beam radiated from the light-emitting portion at a certainradiation angle.

In the first optical transmitter according to the present invention, thesubstrate may be a lead frame for providing a connection to an outsideelectric circuit. Examples of lead frames include one mentioned later inEmbodiment 1.

In the first optical transmitter according to the present invention, thelight-emitting element may include an electrode provided around thelight-emitting portion, the electrode electrically connected to the rearsurface of the substrate.

With this constitution, in which the electrode is provided around thelight-emitting portion, the electrode is in surface-to-surface contactwith the rear surface of the substrate, which is a heat-dissipatingmedium. Heat generated at the light-emitting portion, therefore, can bequickly transmitted to the substrate. Thus, heat dissipation of thelight-emitting element is further improved.

In the first optical transmitter according to the present invention, thethrough hole may comprise a first inner-wall portion provided on therear surface side of the substrate and a second inner-wall portionprovided on the front surface side of the substrate, the firstinner-wall portion having an inside diameter gradually increasing towardthe front surface side of the substrate, the second inner-wall portionhaving an inside diameter greater than a maximum inside-diameter of thefirst inner-wall portion. With this constitution, the through hole canbe formed by forming the second inner-wall portion, having a greaterinside diameter, and then forming the first inner-wall portion. Thus,the processability of the through hole is improved. Also, the use of athick substrate leads to an improvement in heat dissipation of thelight-emitting element.

In the first optical transmitter according to the present invention, theinner wall of the through hole may be concavely curved. With thisconstitution, the optical path of a light beam radiated from thelight-emitting element can be easily changed so that the light beamrises from the substrate substantially perpendicularly irrespective ofthe radiation angle of the light beam. Thus, the coupling efficiency canbe further increased.

In the first optical transmitter according to the present invention, thesubstrate may have a thickness of 50 to 500 μm. With this constitution,miniaturization of the optical transmitter can be achieved. Such a thinsubstrate can be used because the inner wall of the through hole isarranged close to the light-emitting portion of the light-emittingelement, so that the depth of the through hole involved in reflection ofa light beam having a wide radiation angle toward the front surface ofthe substrate can be reduced to a minimum.

The first optical transmitter according to the present invention mayfurther comprise an auxiliary substrate arranged so that thelight-emitting element is sandwiched between the auxiliary substrate andthe substrate, the light-emitting element having a rear electrode on arear surface thereof opposite the light-emitting portion, the rearelectrode electrically connected to the auxiliary substrate. With thisconstitution, the rear electrode of the light-emitting element is insurface-to-surface contact with the auxiliary substrate. Heat generatedat the light-emitting portion, therefore, is dissipated not only fromthe light-emitting portion but also from the rear surface. Thus, heatdissipation of the light-emitting element is further improved. Here,examples of auxiliary substrates include one mentioned later inEmbodiment 3.

The first optical transmitter according to the present invention mayfurther comprise an encapsulating resin-member provided on the rearsurface side of the substrate for encapsulating the light-emittingelement. With this constitution, the light-emitting element can beshielded from the outside air, so that its degradation with time can beretarded.

In the above constitution in which the encapsulating resin-member isprovided, the encapsulating resin-member may be made of a resin, theresin containing a filler for lowering a linear expansivity of theencapsulating resin-member and for raising a thermal conductivitythereof. With this constitution, in which the filler is contained in theresin, which forms the encapsulating resin-member, the linearexpansivity and the thermal conductivity of the resin can be easilychanged so as to reduce thermal stress created on the light-emittingelement and to improve heat dissipation of the light-emitting element.Also, the encapsulating resin-member is provided in an area other thanthe optical path of the optical element, so that thermal stress and heatdissipation can be improved without damaging the optical properties.

The first optical transmitter according to the present invention mayfurther comprise a transparent resin filled in the through hole andcovering the light-emitting surface of the light-emitting element. Withthis constitution, in which the light-emitting surface of thelight-emitting element is covered with the transparent resin, anincreased quantity of light beams can be taken out from thelight-emitting element for the reason mentioned later in Embodiment 1.Further, the light-emitting surface can be shielded from the outsideair, so that its degradation with time can be retarded.

In the above constitution in which the transparent resin is filled inthe through hole, the first optical transmitter may further comprise alens bonded by the transparent resin filled in the through hole so thatthe lens faces the through hole of the substrate.

In the above constitution in which the transparent resin is filled inthe through hole, the transparent resin preferably has a hardness of 50degrees or lower according to JIS-A. With this constitution, in whichthe transparent resin has resiliency, thermal stress created on thelight-emitting element can be reduced, so that the first opticaltransmitter can be used over a wide temperature range. If a lens isprovided, thermal stress created on the lens can be reduced, so that thefirst optical transmitter can be used over a wide temperature range.

The first optical transmitter according to the present invention mayfurther comprise a light-transmissive resin member provided on the frontsurface side of the substrate so as to be filled in the through hole,the light-transmissive resin member having a lens formed as a partthereof for collecting light beams radiated from the light-emittingelement. With this constitution, an increased quantity of light beamscan be taken out from the light-emitting element for the reasonmentioned later in Embodiment 1.

In the structure in which the light-transmissive resin member isprovided on the front surface side of the substrate, the substrate mayhave a resin-injection groove formed in the front surface thereof, theresin-injection groove communicating with the through hole forfacilitating the flow of a light-transmissive resin into the throughhole at the formation of the light-transmissive resin member.

In another aspect, the present invention provides a second opticaltransmitter comprising: a substrate having an opening; a submountattached to the substrate and having a through hole; and alight-emitting element disposed on a rear surface of the submount andhaving a light-emitting portion, the through hole having an inner wall,the through hole having an inside diameter increasing from a rearsurface side of the submount toward a front surface side thereof, thelight-emitting element disposed so that the light-emitting portion isexposed within the through hole, the light-emitting portion radiatinglight beams toward the opening of the substrate, the through hole beingsuch that part of the light beams goes out the through hole and entersthe opening of the substrate without being reflected, and that the otherlight beams goes out the through hole into the opening of the substrateafter being reflected from the inner wall thereof.

The second optical transmitter according to the present inventionprovides the same effect as is obtained by the first optical transmitterin which the through hole is formed in the substrate. Unlike thesubstrate, the submount will suffice if it is of such a size that thelight-emitting element can be disposed thereon, so that the amount of amaterial for the submount can be less. Therefore, even the use of anexpensive material for the submount does not significantly affect thecost, but rather provides a favorable effect of further improving heatdissipation of the light-emitting element.

In the second optical transmitter according to the present invention, adifference in linear expansivity between the submount and thelight-emitting element may be set smaller than a difference in linearexpansivity between the substrate and the light-emitting element. Withthis constitution, the light-emitting element is arranged close to thesubmount having a linear expansivity similar to that of thelight-emitting element. As a result, thermal stress created on thesubmount can be reduced, so that the first optical transmitter can beused over a wide temperature range.

In the second optical transmitter according to the present invention,the submount may be made of silicon, the silicon anisotropically etchedto form the through hole. With this constitution, the through hole canbe provided with the inner wall excellent in plane accuracy and thus inreflection performance.

In the second optical transmitter according to the present invention,the substrate may be a lead frame for providing a connection to anoutside electric circuit.

In the second optical transmitter according to the present invention,the light-emitting element may include an electrode provided around thelight-emitting portion, the electrode electrically connected to the rearsurface of the submount. With this constitution, in which the electrodeis provided around the light-emitting portion, the electrode is insurface-to-surface contact with the rear surface of the submount, whichis a heat-dissipating medium. Heat generated at the light-emittingportion, therefore, can be quickly transmitted to the submount. Thus,heat dissipation of the light-emitting element is further improved.

In the second optical transmitter according to the present invention,wherein the through hole may comprise a first inner-wall portionprovided on the rear surface side of the submount and a secondinner-wall portion provided on the front surface side of the submount,the first inner-wall portion having an inside diameter graduallyincreasing toward the front surface side of the submount, the secondinner-wall portion having an inside diameter greater than a maximuminside-diameter of the first inner-wall portion. With this constitution,the through hole can be formed by forming the second inner-wall portion,having a greater inside diameter, and then forming the first inner-wallportion. Thus, the processability of the through hole is improved. Also,by employing a thick submount, heat dissipation of the light-emittingelement can be improved.

In the second optical transmitter according to the present invention,the inner wall of the through hole may be concavely curved. With thisconstitution, the optical path of a light beam radiated from thelight-emitting element can be easily changed so that the light beamrises from the substrate substantially perpendicularly irrespective ofthe radiation angle of the light beam. Thus, the coupling efficiency canbe further increased.

In the second optical transmitter according to the present invention,the submount has a thickness of 50 to 500 μm. With this constitution,miniaturization of the optical transmitter can be achieved. The reasonwhy such a thin submount can be used is the same as is the case of thefirst optical transmitter in which the through hole is formed in thesubstrate.

The second optical transmitter according to the present invention mayfurther comprise an auxiliary substrate arranged so that thelight-emitting element is sandwiched between the auxiliary substrate andthe submount, the light-emitting element having a rear electrode on arear surface thereof opposite the light-emitting portion, the rearelectrode electrically connected to the auxiliary substrate. With thisconstitution, the rear electrode of the light-emitting element is insurface-to-surface contact with the auxiliary substrate. Heat generatedat the light-emitting portion, therefore, is dissipated not only fromthe light-emitting portion but also from the rear surface. Thus, heatdissipation of the light-emitting element is further improved.

The second optical transmitter according to the present invention mayfurther comprise an encapsulating resin-member provided on a rearsurface side of the substrate for encapsulating the submount and thelight-emitting element. With this constitution, the light-emittingelement and the submount can be shielded from the outside air, so thatits degradation with time can be retarded.

In the above constitution in which the encapsulating resin-member isprovided, the encapsulating resin-member may be made of a resin, theresin containing a filler for lowering a linear expansivity of theencapsulating resin-member and for raising a thermal conductivitythereof. With this constitution, in which the filler is contained in theresin, which forms the encapsulating resin-member, the linearexpansivity and the thermal conductivity of the resin can be easilychanged so as to reduce thermal stress created on the light-emittingelement and on the submount and to improve heat dissipation of thelight-emitting element and the submount. Also, the encapsulatingresin-member is provided in an area other than the optical path of theoptical element, so that thermal stress and heat dissipation can beimproved without damaging the optical properties.

The second optical transmitter according to the present invention mayfurther comprise a transparent resin filled in the through hole and inthe opening and covering the light-emitting surface of thelight-emitting element. With this constitution, in which thelight-emitting surface of the light-emitting element is covered with thetransparent resin, an increased quantity of light beams can be taken outfrom the light-emitting element for the reason mentioned later inEmbodiment 1. Further, the light-emitting surface can be shielded fromthe outside air, so that its degradation with time can be retarded.

In the above constitution in which the transparent resin is filled inthe through hole and in the opening, the second optical transmitter mayfurther comprise a lens bonded by the transparent resin filled in thethrough hole and in the opening so that the lens faces the opening ofthe substrate.

In the above constitution in which the transparent resin is filled inthe through hole and in the opening, the transparent resin preferablyhas a hardness of 50 degrees or lower according to JIS-A. With thisconstitution, in which the transparent resin has resiliency, thermalstress created on the light-emitting element can be reduced, so that thesecond optical transmitter can be used over a wide temperature range. Ifa lens is provided, thermal stress created on the lens can be reduced,so that the second optical transmitter can be used over a widetemperature range.

The second optical transmitter according to the present invention mayfurther comprise a light-transmissive resin member provided on a frontsurface side of the substrate so as to be filled in the through hole andin the opening, the light-transmissive resin member having a lens formedas a part thereof for collecting light beams radiated from thelight-emitting element. With this constitution, an increased quantity oflight beams can be taken out from the light-emitting element for thereason mentioned later in Embodiment 1.

In the constitution in which the light-transmissive resin member isprovided on a front surface side of the substrate, the substrate mayhave a resin-injection groove formed in the front surface thereof, theresin-injection groove communicating with the opening for facilitatingthe flow of a light-transmissive resin into the opening and into thethrough hole communicating therewith at the formation of thelight-transmissive resin member.

In still another aspect, the present invention provides a third opticaltransmitter comprising: a substrate having a first through hole; asubmount attached to the substrate and having a second through hole; anda light-emitting element disposed on a rear surface of the submount andhaving a light-emitting portion, the first through hole having an innerwall, the first through hole having an inside diameter increasing from arear surface side of the substrate toward a front surface side thereof,the second through hole having an inner wall, the second through holehaving an inside diameter increasing from a rear surface side of themount toward a front surface side thereof, the light-emitting elementdisposed so that the light-emitting portion is exposed within the secondthrough hole, the light-emitting portion radiating light beams toward afront surface of the substrate, the first through hole and the secondthrough hole being such that part of the light beams goes out the firstthrough hole without being reflected, and that the other light beams goout the first through hole after being reflected from at least one ofthe inner wall of the substrate and the inner wall of the submount.

The third optical transmitter according to the present inventionprovides the same effect as is obtained by the first opticaltransmitter, in which the through hole is formed in the substrate alone,or by the second optical transmitter in which the through hole is formedin the submount alone. Especially because the two through holes can begiven different shapes, arbitrarily selecting the shape of each throughhole depending on the radiation pattern of the light-emitting elementmakes it is possible to obtain an effect that the transmissionefficiency can be further improved. In the third optical transmitteraccording to the present invention, the first through hole communicatewith the second through hole, and preferably, the first through hole hasa minimum inside diameter the same as or slightly greater than a maximuminside diameter of the second through hole.

In the third optical transmitter according to the present invention, adifference in linear expansivity between the submount and thelight-emitting element may be set smaller than a difference in linearexpansivity between the substrate and the light-emitting element. Withthis constitution, the light-emitting element is arranged close to thesubmount having a linear expansivity similar to that of thelight-emitting element. As a result, thermal stress created on thesubmount can be reduced, so that the first optical transmitter can beused over a wide temperature range.

In the third optical transmitter according to the present invention, anangle formed between the inner wall of the first through hole and anoptical axis of the light-emitting element may be set smaller than anangle formed between the inner wall of the second through hole and theoptical axis of the light-emitting element. With this constitution, oflight beams radiated from the light-emitting portion, a light beamhaving a wide radiation angle is applied onto the inner wall of thesecond through hole, while a light beam having a narrow radiation angleis applied onto the inner wall of the first through hole. By setting theangle formed between the inner wall of the first through hole and theoptical axis of the light-emitting element smaller than the angle formedbetween the inner wall of the second through hole and the optical axisof the light-emitting element, the optical paths of the light beamhaving a wide radiation angle and the light beam having a narrowradiation angle emitted from the light-emitting element light-emittingelement both can be changed perpendicularly with respect thelight-emitting surface of the light-emitting element. Thus, hightransmission efficiency can be obtained.

In the third optical transmitter according to the present invention, thesubmount may be made of silicon, the silicon anisotropically etched toform the through hole. With this constitution, the submount can beprovided with the inner wall excellent in plane accuracy and thus inreflection performance.

In the third optical transmitter according to the present invention, thelight-emitting element may include an electrode provided around thelight-emitting portion, the electrode electrically connected to the rearsurface of the submount. With this constitution, in which the electrodeis provided around the light-emitting portion, the electrode is insurface-to-surface contact with the rear surface of the submount, whichis a heat-dissipating medium. Heat generated at the light-emittingportion, therefore, can be quickly transmitted to the submount. Thus,heat dissipation of the light-emitting element is further improved.

In the third optical transmitter according to the present invention, thesubstrate may be a lead frame for providing a connection to an outsideelectric circuit.

In the third optical transmitter according to the present invention, thefirst through hole may comprise a first inner-wall portion provided onthe rear surface side of the substrate and a second inner-wall portionprovided on the front surface side of the substrate, the firstinner-wall portion having an inside diameter gradually increasing towardthe front surface side of the substrate, the second inner-wall portionhaving an inside diameter greater than a maximum inside-diameter of thefirst inner-wall portion. With this constitution, the first through holecan be formed by forming the second inner-wall portion, having a greaterinside diameter, and then forming the first inner-wall portion. Thus,the processability of the first through hole is improved. Also, byemploying a thick substrate, heat dissipation of the light-emittingelement can be improved.

In the third optical transmitter according to the present invention, thesecond through hole may comprise a first inner-wall portion provided onthe rear surface side of the submount and a second inner-wall portionprovided on the front surface side of the submount, the first inner-wallportion having an inside diameter gradually increasing toward the frontsurface side of the submount, the second inner-wall portion having aninside diameter greater than a maximum inside-diameter of the firstinner-wall portion. With this constitution, the second through hole canbe formed by forming the second inner-wall portion, having a greaterinside diameter, and then forming the first inner-wall portion. Thus,the processability of the second through hole is improved. Also, byemploying a thick submount, heat dissipation of the light-emittingelement can be improved.

In the third optical transmitter according to the present invention, theinner wall of either the first through hole or the second through holemay be concavely curved. With this constitution, the optical path of alight beam radiated from the light-emitting element can be easilychanged so that the light beam rises from the substrate substantiallyperpendicularly irrespective of the radiation angle of the light beam.Thus, the coupling efficiency can be further increased.

In the third optical transmitter according to the present invention, thesubstrate and the submount each may have a thickness of 50 to 500 μm.With this constitution, miniaturization of the optical transmitter canbe achieved. The reason why such a thin submount and a substrate can beused is the same as is the case of the first optical transmitter inwhich the through hole is formed in the substrate.

The third optical transmitter according to the present invention mayfurther comprise an auxiliary substrate arranged so that thelight-emitting element is sandwiched between the auxiliary substrate andthe submount, the light-emitting element having a rear electrode on arear surface thereof opposite the light-emitting portion, the rearelectrode electrically connected to the auxiliary substrate. With thisconstitution, the rear electrode of the light-emitting element is insurface-to-surface contact with the auxiliary substrate. Heat generatedat the light-emitting portion, therefore, is dissipated not only fromthe light-emitting portion but also from the rear surface. Thus, heatdissipation of the light-emitting element is further improved.

The third optical transmitter according to the present invention mayfurther comprise an encapsulating resin-member provided on the rearsurface side of the substrate for encapsulating the submount and thelight-emitting element. With this constitution, the light-emittingelement and the submount can be shielded from the outside air, so thatits degradation with time can be retarded.

In the above constitution in which the encapsulating resin-member isprovided, the encapsulating resin-member may be made of a resin, theresin containing a filler for lowering a linear expansivity of theencapsulating resin-member and for raising a thermal conductivitythereof. With this constitution, in which the filler is contained in theresin, which forms the encapsulating resin-member, the linearexpansivity and the thermal conductivity of the resin can be easilychanged so as to reduce thermal stress created on the light-emittingelement and on the submount and to improve heat dissipation of thelight-emitting element and the submount. Also, the encapsulatingresin-member is provided in an area other than the optical path of theoptical element, so that thermal stress and heat dissipation can beimproved without damaging the optical properties.

The third optical transmitter according to the present invention mayfurther comprise a transparent resin filled in the first through holeand in the second through hole and covering the light-emitting surfaceof the light-emitting element. With this constitution, in which thelight-emitting surface of the light-emitting element is covered with thetransparent resin, an increased quantity of light beams can be taken outfrom the light-emitting element for the reason mentioned later inEmbodiment 1. Further, the light-emitting surface can be shielded fromthe outside air, so that its degradation with time can be retarded.

In the above constitution in which the transparent resin is provided,the third optical transmitter may further comprise a lens bonded by thetransparent resin filled in the first through hole and in the secondthrough hole so that the lens faces the first through hole of thesubstrate.

In the above constitution in which the transparent resin is provided,the transparent resin preferably has a hardness of 50 degrees or loweraccording to JIS-A. With this constitution, in which the transparentresin has resiliency, thermal stress created on the light-emittingelement can be reduced, so that the first optical transmitter can beused over a wide temperature range. If a lens is provided, thermalstress created on the lens can be reduced, so that the first opticaltransmitter can be used over a wide temperature range.

The third optical transmitter according to the present invention mayfurther comprise a light-transmissive resin member provided on a frontsurface side of the substrate so as to be filled in the first throughhole and in the second through hole, the light-transmissive resin memberhaving a lens formed as a part thereof for collecting light beamsradiated from the light-emitting element. With this constitution, anincreased quantity of light beams can be taken out from thelight-emitting element for the reason mentioned later in Embodiment 1.

In the above constitution in which the light-transmissive resin memberis provided on the front surface side of the substrate, the substratemay have a resin-injection groove formed in the front surface thereof,the resin-injection groove communicating with the first through hole forfacilitating the flow of a light-transmissive resin into the firstthrough hole and into the second through hole communicating therewith atthe formation of the light-transmissive resin member.

In yet another aspect, the present invention provides an illuminationdevice comprising a plurality of optical transmitters arranged side byside, each optical transmitters as set forth above.

Hereafter, embodiments of the present invention are shown in detailreferring to the drawings. In the embodiments, like reference numeralsdenote members having like functions.

Embodiment 1

FIG. 1 is an explanatory view showing a schematic construction of anoptical transmitter according to Embodiment 1 of the present invention.

The optical transmitter 1 comprises a light-emitting element 3, a lens 4and a lead frame (substrate) 5 disposed on the light-emitting element 3.

The lead frame 5 has a through hole 7 formed in a position facing alight-emitting surface (light-emitting portion) 6 of the light-emittingelement 3. The through hole 7 is tapered so that its inside diametergradually increases from a rear surface side, on which thelight-emitting element 3 is disposed, toward a front surface side. Thetapered through hole 7 has an inner wall called a taper mirror 8.

Of light beams radiated from the light-emitting element 3, a light beamhaving a narrow radiation angle passes through the through hole 7 andenters the lens 4 to be refracted and coupled into an optical fiber 2. Alight beam having a wide radiation angle of the light beams radiatedfrom the light-emitting element 3, on the other hand, is reflected fromthe taper mirror 8 and enters the lens 4 to be refracted and coupledinto the optical fiber 2.

Therefore, even the use of, for example, an LED having a wide radiationangle as the light-emitting element 3 makes possible coupling of lightbeams from the light-emitting element 3 into the optical fiber 2 withhigh efficiency.

The light-emitting element 3 is positioned so that its light-emittingsurface 6 faces the through hole 7 of the lead frame 5, and bonded tothe lead frame 5 by an electrically conductive adhesive such as a silverpaste or with a eutectic of gold and tin or of other materials.

That is, an electrode (see, e.g., a p-electrode 15 of FIG. 3) of thelight-emitting element 3 on the light-emitting surface 6 side iselectrically continuous with the lead frame 5. The lead frame 5 iselectrically continuous with a circuit substrate, not illustrated.

The light-emitting element 3 is covered with a mold resin(light-transmissive resin member) 9 made of, for example, an epoxy resinor an acrylic resin. The lens 4 is also formed of the mold resin 9.

Also, in addition to the light-emitting element 3, a driver IC, notillustrated, for driving the light-emitting element 3, and the like, aredisposed on the lead frame 5 and are also encapsulated in the mold resin9.

If the light-emitting element 3 is one having a relatively wideradiation angle such as an LED, the light-emitting element 3 ispreferably covered with the mold resin 9 as shown in FIG. 1.

A light beam from the light-emitting element 3 is refracted due to thedifference in refractive index between the surface of the light-emittingelement 3 and the outside (air or the mold resin 9) before the lightbeam is radiated. Therefore, an increased quantity of light beams can betaken out when the light-emitting element 3 is covered with the moldresin 9 than when the light-emitting element 3 is covered with air therefractive index of which is smaller. This is because the angle at whichtotal reflection occurs is a greater when the light-emitting element 3is covered with the mold resin 9.

For example, changing the refractive index of the outside from 1 to 1.56achieves about 2.4-fold increase in the quantity of light beams from thelight-emitting element 3. Therefore, covering the light-emitting element3 with the mold resin 9 increases the utility efficiency of light beams.Also, shielding the light-emitting element 3, the driver IC and othercomponents from the outside makes possible retarding degradation withtime.

The light-emitting element 3 is preferably a light emitting diode (LED)of surface-emitting type. FIG. 2 and FIG. 3 show an LED of traditionaldouble hetero structure.

As shown in FIG. 3, an n-electrode 11 is formed on a lower surface of ann-type substrate 10 made of GaAs or the like. On the n-type substrate10, there are formed an n-type cladding layer 12, an active layer 13, ap-type cladding layer 14 and the p-electrode 15 in this order.

As shown in FIG. 2 and FIG. 3, in the p-electrode 15, there is formed anopening, from which the light-emitting surface 6 is exposed, and lightbeams are emitted from the light-emitting surface 6.

The structure and the material of the light-emitting element 3 each arearbitrarily selected depending on the wavelengths and thecharacteristics demanded. In the below, explanation is made on thepremise that the light-emitting element 3 is an LED of the structureshown in FIG. 2 and FIG. 3. However, needless to say, the presentinvention can also be achieved using the light-emitting element 3 ofanother structure.

One feature of the present invention is that the through hole 7 in thelead frame 5 has the taper mirror 8 in order for light beams having wideradiation angles to be raised from the surface of the lead frame 5. Thetaper mirror 8 makes it possible to miniaturize the optical transmitter1 and reduce the cost thereof and also contributes to increasing theoptical transmission efficiency, to reducing the variation in opticaltransmission efficiency, and to improving heat dissipation of thelight-emitting element 3. Hereafter, explanation is given to theseeffects.

Referring to FIG. 1, FIG. 4 and FIG. 5, the size of the opticaltransmitter 1 according to Embodiment 1 is compared with that of theconventional optical transmitter 201 of FIG. 23 for explanation. FIG. 4is an enlarged view of an essential part of the optical transmitter 1 ofFIG. 1. FIG. 5 is an explanatory view in which the size of the opticaltransmitter 1 according to Embodiment 1 shown in FIG. 1 is compared withthat of the conventional optical transmitter 201 shown in FIG. 23 on thesame figure. In FIG. 5, the conventional optical transmitter 201 isindicated by the dashed lines.

As aforementioned, in the conventional optical transmitter 201 shown inFIG. 23, assuming that: the LED 103 is in the shape of a cube with aheight of 300 μm and a width of 300 μm; the concave mirror 108 has ataper angle θ of 60°; and the concave portion has an inside diameter ofφ 500 μm on the bottom surface side thereof, the concave portion needsto have a depth T0 of about 1.3 mm and an inside diameter R0 of 2 mm onthe upper edge side in order for the concave mirror 108 to change theoptical path of a light beam having a radiation angle of 45° or wider,of light beams radiated from the center of the light-emitting surface106 of the LED 103.

On the other hand, in the optical transmitter 1 according to Embodiment1 shown in FIG. 1, if calculation is made on the assumption that thethrough hole 7 has an inside diameter of about φ 100 μm on the rearsurface side thereof, and that the other conditions are the same asthose of the prior art shown in FIG. 23, it is found that, as shown inFIG. 4, a thickness T1 of the lead frame 5, corresponding to the depthT0 (see FIG. 23) of the concave portion of the prior art is 0.12 mm, andan inside diameter R1 of the through hole 7 on the front surface sidethereof, corresponding to the inside diameter R0 (see FIG. 23) on theupper edge side of the prior art, is about 0.24 mm. Thus, the presentinvention achieves a reduction in both thickness and size to about1/10^(th) of the prior art.

As is clear from FIG. 5, according to Embodiment 1 in which the insidediameter R1 of the through hole 7 on the front surface side thereof canbe as small as about 0.24 mm, the lens 4 (see FIG. 1) for collectinglight beams onto the optical fiber also can have a reduced diameter.

Accordingly, there is a high degree of design freedom of the lens 4,making it easy to obtain the lens 4 which has performance ideal incoupling light beams raised from the front surface side of the throughhole 7 into the optical fiber 2 with high efficiency.

Also, the lead frame 5 usually has a thickness of about 0.25 mm, so thatthe optical transmitter 1 can be of the same size as that of the opticaltransmitter 101, shown in FIG. 21, which is produced by transfer mold.

On the other hand, with the conventional optical transmitter 201 shownin FIG. 23, in which the inside diameter R0 of the concave portion onthe upper edge side thereof is as large as about φ 2 mm, the possibilityarises: the use of a lens with a short focal length may cause thefailure of light beams to be coupled into the optical fiber because anNA incident to the optical fiber becomes too large, while the use of alens with a long focal length in order to take an advantage of a smallincident NA may make it difficult to miniaturize the optical transmitterinclusive of the optical fiber. Thus, it is difficult to increase thecoupling efficiency while achieving miniaturization and cost reductionof the optical transmitter.

Further, there is another problem that a space for wire-bonding anelectrode of the LED 103 needs to be provided at a portion of theconcave mirror 108, which complicates the production process.

In contrast to this, according to the present invention, in which thetaper mirror 8 is arranged significantly close to the light-emittingsurface 7, and the lead frame 5 is provided with the taper mirror 8, itis possible to increase the transmission efficiency and miniaturize theoptical transmitter 1.

According to the present invention, it is possible to achieveminiaturization of the optical transmitter 1 while increasing theefficiency of coupling from the light-emitting element 3 into theoptical fiber 2, which is conventionally difficult.

In the optical transmitter 1 according to Embodiment 1, the through hole7 can be formed by etching or pressing simultaneously with thepatterning-processing of the lead frame 5 without incurring a rise incost. Accordingly, the optical transmitter 1 can be obtained at a lowcost.

Here, it is preferable to form, simultaneously with the formation of thethrough hole 7, a reference hole, not illustrated, for positioning thelight-emitting element 3, the lens 4 and the optical fiber 2 withrespect to one another. By using this reference hole as a reference inassembling the optical transmitter 1, it is possible to position thethrough hole 7, the light-emitting element 3, the lens 4 and the opticalfiber 2 with respect to one another.

Next, explanation is given to the through hole 7. The inside diameter ofthe through hole 7 of the lead frame 5 on the rear surface side ispreferably slightly greater or slightly smaller than the diameter of thelight-emitting surface 6 of the light-emitting element 3. Whether tomake the inside diameter of the through hole 7 greater or smaller isdecided depending on whether to assign higher priority to increasing thetransmission efficiency or to reducing the variation in transmissionefficiency.

If higher priority is assigned to increasing the transmissionefficiency, it is preferable to make slightly greater the insidediameter of the through hole 7 on the rear surface side than thediameter of the light-emitting surface 6 of the light-emitting element3. If the diameter of the light-emitting surface 6 is φ 70 μm forexample, the inside diameter of the through hole 7 on the rear surfaceside is set at about 100 μm. Thus, it is ensured that even if thelight-emitting element 3 comes off position with respect to the throughhole 7, light beams emitted from the light-emitting surface 6 are notkicked by the lead frame 5, so that all the light beams radiated fromthe light-emitting surface 6 can be utilized.

On the other hand, if higher priority is assigned to reducing thevariation in transmission efficiency, it is preferable to make slightlysmaller the inside diameter of the through hole 7 on the rear surfaceside than the diameter of the light-emitting surface 6 of thelight-emitting element 3. If the diameter of the light-emitting surface6 is φ 70 μm for example, the inside diameter of the through hole 7 onthe rear surface side is set at 50 μm. This ensures that even if thelight-emitting element 3 comes off position, the quantity of light beamspassing through the through hole 7 is less varied, so that the variationin transmission efficiency can be reduced.

Also, in the optical transmitter 1 according to Embodiment 1, the tapermirror 8 can be arranged closer to the light-emitting surface 6 than inthe conventional optical transmitter shown in FIG. 23. This ensures thateven if the light-emitting element 3 comes off position, the position atwhich a light beam is raised is less varied, so that the variation inthe efficiency of coupling of light beams into the lens 4 and into theoptical fiber 2 can be reduced.

Examples of shapes of the through hole 7 include ones shown in FIGS. 6to 13.

The through hole 7 shown in FIGS. 6 and 7, like the one shown in FIG. 1,has the taper mirror 8 of linear cross section.

The taper mirror 8 of linear cross section is easy to process andensures that, of light beams radiated from the light-emitting element 3,the optical path of even a light beam with a wide radiation angle can bechanged.

Here, the taper angle θ (see FIG. 4) is preferably about 40° to 80° tosuit the far field pattern of light beams emitted from thelight-emitting element 3. The optimal taper angle is decided dependingon the far field pattern of light beams emitted from the light-emittingelement 3 used.

Further, the taper mirror 8 is preferably of curved (i.e., concave)cross section as shown in FIGS. 8 and 9.

For example, if the taper mirror 8 is of parabola-shaped cross sectionand the light-emitting surface 6 is arranged at the focal point of theparabola, it is possible to change the optical path of a light beamradiated from the light-emitting element 3 substantially perpendicularlywith respect to the lead frame 5, irrespective of radiation angle of thelight beam. Such a curved shape can be obtained by, for example, etchingthe lead frame 5 from one side.

Also, the through hole 7 is preferably of the shape shown in FIGS. 10and 11. That is, the through hole 7 preferably includes a taper mirror(first inner-wall) portion 8 on the rear surface side of the lead frame5 and an enlarged hole (second inner-wall) portion 17 on the frontsurface side of the lead frame 5. The taper mirror portion 8 has aninside diameter gradually increasing toward the front surface side ofthe lead frame 5. The enlarged hole portion 17 has an inside diametergreater than the maximum inside diameter of the taper mirror portion 8.

In the through hole 7 shown in FIGS. 10 and 11, the enlarged holeportion 17 has the effects of improving heat dissipation of thelight-emitting element 3 and improving the processability of the tapermirror 8.

That is, it is difficult to process the through hole 7 if the thicknessof the lead frame 5 is much greater than the inside diameter of thethrough hole 7 on the rear surface side, which as mentioned above isabout 100 μm. In contrast, as the thickness of the lead frame 5 becomesgreater, there is a more advantage in heat dissipation of thelight-emitting element 3 and of the driver IC for driving thelight-emitting element 3.

Thus, by forming the enlarged hole portion 17 in the lead frame 5 on thefront surface side thereof, the processing of the taper mirror portion 8is facilitated and the lead frame 5 is allowed to have a greaterthickness, resulting in an improvement in heat dissipation. The enlargedhole portion 17, which is not irradiated with any light beam, does nothave any optical role.

It is preferable to form a resin-injection groove 18 in the frontsurface side of the lead frame 5 in such a manner that theresin-injection groove 18 communicates with the through hole 7 as shownin FIGS. 12 and 13.

That is, forming the resin-injection groove 18 eliminates the difficultycaused in flowing the resin into the through hole 7 for moldencapsulation with the mold resin 9 as shown in FIG. 1. Thus, the moldencapsulation is ensured. The enlarged hole portion 17 shown in FIGS. 10and 11 provides the same effect as obtained by the resin-injectiongroove 18.

Further, it is preferable to set the thickness and the taper angle ofthe lead frame 5 so that a light beam is reflected from the taper mirror8 only once. In the case of the so-called optical wave-guide or the likeutilizing a plurality of reflections, a greater loss is produced due tothe reflections, and the length (equivalent to the thickness of the leadframe 5) is increased, which results in upsizing of devices.

According to the present invention, the shape of the through hole 7 canbe modified in various ways as described above, though the depth of thethrough hole 7 is preferably set at 50 to 500 μm.

That is, according to the present invention, since the taper mirror 8can be arranged close to the light-emitting surface 6, the through hole7 ensures a sufficient effect in changing the optical path of a lightbeam with a wide radiation angle even if the depth of the through hole 7is small.

Also, when seen from the front surface or the rear surface of the leadframe 5, the through hole 7 does not necessarily need to be circular inshape but may be elliptical or square. The through hole 7 isadvantageously of a shape other than a circular shape if there is, forexample, distortion in the far field pattern of light beams from thelight-emitting element 3.

According to the present invention, as described above, thelight-emitting element 3 is disposed on the rear surface side of thelead frame 5. The through hole 7 is basically of tapered cross sectionso that its inside diameter thereof gradually increases from the rearsurface side of the lead frame toward the front surface side thereof.

Also, the inside diameter of the through hole 7 on the rear surface sideis set smaller than the size of the light-emitting element 3 chip. Asthe inside diameter of the through hole 7 is reduced when compared withthe size of the light-emitting element 3 chip, the contact area betweenthe light-emitting element 3 and the lead frame 5 increases.

It is important in improving heat dissipation of the light-emittingelement 3 that the light-emitting element 3 is disposed so that thelight-emitting surface 7 faces the lead frame 5 and that there is alarge contact area between the light-emitting element 3 and the leadframe 5.

That is, the thermal resistance of the n-type substrate 10 becomes aproblem when using the LED shown in FIGS. 2 and 3 as the light-emittingelement 3.

If heat is dissipated from the rear surface side (n-electrode 11 side)of the LED, heat generated at the active layer 13 is dissipated via then-type substrate 10 and further via the n-electrode 11 into the leadframe 5 and the like, which are each made of a material good in heatdissipation.

Since the n-type substrate 10 is usually made of a material having ahigh thermal resistance such as GaAs, the LED itself is poor in heatdissipation, resulting in an increased temperature of the active layer13.

In contrast, in the present invention, in which the light-emittingsurface 7 faces the lead frame 5, heat generated at the active layer 13can be dissipated via the p-type cladding layer 14 and then via thep-electrode 15 into the lead frame 5. When compared with the thermalconductivity of, for example, GaAs, which is 45 W/m·K, the thermalconductivity of the lead frame 5 (copper) is as high as about 360 W/m·K.Further, since the p-type cladding layer 14 and the p-electrode 15 eachhave a thickness of about several μm, heat dissipation is significantlyimproved when compared with the case where heat is dissipated via then-type substrate 10 having a thickness of several hundreds of μm.

The light-emitting element 3 and the lead frame 5 are preferably bondedtogether by, for example, an adhesive having high conductivity such as asilver paste, or a eutectic of either gold and tin or of othermaterials. Also, among adhesives having high conductivity, morepreferable are ones that ensure sufficient thermal contact with amaterial having a high thermal conductivity or with a material in theform of a thin layer and also that absorb the difference in linearexpansivity between the lead frame 5 and the light-emitting element 3.

Here, it is necessary to avoid sticking of the adhesive to thelight-emitting surface 6 of the light-emitting element 3. A thin layerof the adhesive may be formed beforehand over an area of thelight-emitting element 3 other than the light-emitting surface 6 byphotolithography or another technique so that sticking of the adhesiveto the light-emitting surface 6 is avoided. Alternatively, if theeutectic either of gold and tin or of other materials is used, thelight-emitting element 3 and the lead frame 5 may be bonded together byplating the surface of the lead frame 5 with gold and forming a gold-tinfilm on the p-electrode 15 of the light-emitting element 3, followed bythermocompression bonding.

Hereafter, explanation is given to each component.

The optical fiber 2 is preferably a multimode optical fiber such as aplastic optical fiber (POF: polymer optical fiber) or a quartz glassoptical fiber (GOF: glass optical fiber).

The core of the POF is made of plastic having excellent opticaltransmission properties such as PMMA (polymethylmethaacrylate) orpolycarbonate and the cladding thereof is made of plastic lower inrefractive index than the plastic of the core.

In the POF, it is easier than in the GOF to increase the diameter of thecore from about 200 im to about 1 mm and thus easier to adjust thecoupling with the optical transmitter. Consequently, it is possible toobtain an inexpensive optical communications link.

Alternatively, the optical fiber 2 may be a PCF (polymer clad fiber) inwhich the core is made of a quartz glass and the cladding is made of apolymer.

On the other hand, the GOF is more expensive than the POF though the GOFsuffers a smaller loss of transmission and provides a wider band oftransmission than the POF. Thus, if the GOF is used as a transmissionmedium, it is possible to obtain an optical communications link that canafford longer-distance communication and higher-speed communications.

The light-emitting element 3 is of surface-emitting type and may be alight-emitting diode (LED), a surface emitting laser (VCSEL) or thelike.

The wavelength of the light-emitting element 3 is preferably one thatproduces a smaller loss of transmission of light beams into the opticalfiber 2 used.

For example, if the POF is used as the optical fiber 2, the wavelengthof the light-emitting element 3 may be about 650 nm, while if the GOF isused as the optical fiber 2, the wavelength of the light-emittingelement 3 may be about 850 nm.

The lead frame 5 is obtained by forming the through hole 7 in a thinplate of a metal having a high thermal conductivity such as copper orphosphor bronze by means of etching, pressing or cutting, followed byplating its surface with silver, gold or the like to obtain highreflectance.

Here, the lead frame 5 means a thin plate of a metal that is disposed onand supports components such as the light-emitting element 3 and thedriver IC and that plays a role of transmitting electricity to eachcomponent. Of course, the lead frame 5 may be replaced with varioussubstrates such as a stem and a printed substrate.

Embodiment 2

A modification of the above optical transmitter according to Embodiment1 is given as an optical transmitter according to Embodiment 2 andexplained referring to FIG. 14. FIG. 14 is an explanatory view showing aschematic structure of the optical transmitter according to Embodiment2.

As shown in FIG. 14, in the optical transmitter 21 according toEmbodiment 2, the lens 4 is not formed of the mold resin (encapsulatingresin member) 9. The mold resin 9 covers only the rear surface side ofthe lead frame 5 on which the light-emitting element 3 is disposed. Thelight-emitting element 3 and a driver IC 19 are encapsulated in the moldresin 9 and protected from outside air. The light-emitting element 3 andthe driver IC 19 are electrically connected together with a bonding wire33 (though in the reality there are a plurality of bonding wires 33,omission is made in the figure).

The lens 4 can be a ball lens made of a glass, an acrylic resin or thelike. The ball lens as the lens 4 is positioned with respect to thethrough hole 7 of the lead frame 5 and bonded thereto by an adhesive(transparent resin) 16.

The adhesive 16 is made of a material having transparency in the rangeof wavelengths of the light-emitting element 3. The adhesive 16 isfilled in the through hole 7 and covers the light-emitting surface ofthe light-emitting element 3. Since the through hole 7 is filled withthe adhesive 16, the refractive is increased when compared with the casewhere the air covers the through hole so that an increased quantity oflight beams can be out taken from the light-emitting element 3.

The adhesive 16 is preferably made of a material having resiliency. Thelead frame 5 is made of a metal such as copper and thus is generallysignificantly different from the adhesive 16 in linear expansivity.Accordingly, if the ambient temperature changes, a great thermal stressis created at the interfaces between the adhesive 16 and the lead frame5 and between the light-emitting element 3 and the adhesive 16, theadhesive 16 easily comes off. By using the adhesive 16 made of, forexample, a material having resiliency (i.e., a material having a lowYoung's modulus) such as silicone, thermal stress can be reduced toprevent the adhesive 16 from coming off. For the resiliency of theadhesive 16, the adhesive 16 preferably has a hardness of 50 degrees orlower according to JIS-A. Alternatively, the adhesive 16 preferably hasa Young's modulus of 10 MPa or lower.

Further, the lens 4 is preferably bonded by the adhesive 16 havingresiliency. Though thermal stress is also created on the lens 4 due to achange in ambient temperature, the resiliency of the adhesive 16 servesto reduce thermal stress to make it difficult for the lens 4 to comeoff.

Also, the mold resin 9 does not need to be transparent, and for example,materials having a high thermal conductivity, materials having a linearexpansivity similar to that of the light-emitting element 3 and to thatof the bonding wire 33, as well as inexpensive materials can be used. Atransparent mold resin (in the case of an epoxy resin, generally, linearexpansivity: 60 to 65 ppm/K, thermal conductivity: about 0.2 W/m·K) isgreater in linear expansivity than the light-emitting element 3 (in thecase of GaAs, linear expansivity: 6 ppm/K) and than the bonding wire (inthe case of gold, linear expansivity: about 14 ppm/K). Thus, greatthermal stress is created on the light-emitting element 3 and thebonding wire 33. For this reason, the resin for molding is preferably aresin containing a filler having a low linear expansivity such assilica. Such a resin can be a resin in black color (linear expansivity:15 to 20 ppm/K, thermal conductivity: about 0.7 W/m·K), which isgenerally used in packaging of ICs that require no optical properties.Such resins are in general use and thus available at a low cost.According to the present invention, the difference between each one ofthe light-emitting element 3 and bonding wire 33 and the mold resin 9 inlinear expansivity can be significantly reduced, so that thermal stresscreated on the light-emitting element 3 and the bonding wire 33 can bereduced. Since the filler is contained, the thermal conductivity of theresin itself is increased with the result that heat dissipation of thelight-emitting element 3 and of the driver IC 19 also can be improved.Consequently, the function and the reliability of the opticaltransmitter 1 can be further improved and the cost thereof can befurther reduced. For example, rupture of the wire resulting from adifference in linear expansivity between the lead frame 5 and the moldresin 9 can be prevented.

Embodiment 3

Another modification of the above optical transmitter according toEmbodiment 1 is given as an optical transmitter according to Embodiment3 and explained referring to FIG. 15. FIG. 15 is an enlarged view of anessential part of the optical transmitter according to Embodiment 3.

As shown in FIG. 15, in the optical transmitter 31 according toEmbodiment 3, the through hole 7 is of the shape shown in FIGS. 10 and11.

A light beam emitted from the light-emitting element is reflected fromthe taper mirror portion 8, without being applied onto the inner wall ofthe enlarged hole portion 17, so that the optical path of the light beamis changed.

As aforementioned, this constitution allows the lead frame 5 to have anincreased thickness so that heat dissipation is improved, and furtherthat the effect of the mold resin (light-transmissive resin member) 9 orthe adhesive (transparent resin) 16 easily flowing into the through hole7 can be obtained.

Also, the light-emitting element 3 has, on its rear surface opposite thelight-emitting surface 6, the electrode (see the n-electrode 11 of FIG.3) bonded to a rear-electrode substrate (auxiliary substrate) 22 by anelectrically conductive adhesive such as a silver paste.

The lead frame 5 and the rear-electrode substrate 22 each areelectrically connected to an electric circuit, not illustrated, for theon/off control of the light-emitting element 3.

The rear-electrode substrate 22 is made of a metal having a high thermalconductivity such as aluminum, copper or phosphor bronze.

That is, the light-emitting element 3 is not electrically connected byan elongate member such as a wire. Instead, the electrode (see thep-electrode 15 of FIG. 3) of the light-emitting element 3 on thelight-emitting surface 6 side and the electrode thereof on the rearsurface side are in surface-to-surface contact with the lead frame 5 andthe rear-electrode substrate 22, respectively. Accordingly, heatgenerated at the light-emitting element 3 can be dissipated efficiently,significantly improving heat dissipation.

In Embodiment 3, as in the case of Embodiment 1, the mold resin(light-transmissive resin member) may be provided on the front surfaceside of the lead frame 5 so as to be filled in the through hole 7 and inthe enlarged hole portion 17 and to have the lens formed as an integralpart of the mold resin. Alternatively, as in Embodiment 2, the adhesive(transparent resin) may be filled in the through hole 7 and in theenlarged hole portion 17 and cover the light-emitting surface 6 of thelight-emitting element 3 to bond the lens so that the lens faces theenlarged hole portion 17.

Embodiment 4

Still another modification of the above optical transmitter according toEmbodiment 1 is given as an optical transmitter according to Embodiment4 and explained referring to FIG. 16. FIG. 16 is an enlarged view of anessential part of an optical transmitter according to Embodiment 4 ofthe present invention.

As shown in FIG. 16, in the optical transmitter 41 according toEmbodiment 4, the light-emitting element 3 is disposed on a submount 24so that the submount 24 is interposed between the light-emitting element3 and a second substrate 25.

The submount 24 has the through hole 7 and the taper mirror 8 similar tothe ones formed through the lead frame 5 in Embodiment 1. Thelight-emitting element 3 is positioned so that the light-emittingsurface 6 thereof faces the through hole 7, and is disposed on a rearsurface of the submount 24.

The second substrate 25 has a light-emission hole (opening) 26 greaterthan the through hole of the submount 24. The through hole of thesubmount 24 communicates with the light-emission hole of the secondsubstrate 25.

The submount 24 has the same effect as that of the lead frame 5 and canimprove the optical transmission efficiency due to the function of thetaper mirror 8.

This constitution allows the size of the member having the taper mirror8, i.e., the size of the submount 24 to be kept slightly greater thanthe light-emitting element 3. Therefore, even if an expensive materialis used for the submount 24, it does not significantly affect the cost.

That is, the material of the submount 24 can be selected withoutrestraint and without considering the cost. Thus, by using, for example,a material having a high thermal conductivity or a material having highprocessability, it is possible to easily further improve the performanceand the reliability of the optical transmitter 41.

The submount 24 is preferably obtained by processing a single-crystalsilicon substrate through anisotropic etching.

A (111) plane having an angle of 54.74° is obtained as a smooth surfacehaving a precise angle by, for example, etching a (100) plane of thesingle-crystal silicon with KOH (potassium hydroxide).

That is, the taper mirror 8 (see FIG. 4) obtained by processing the leadframe 5 is inferior to the taper mirror 8 obtained by processing thesingle-crystal silicon in processing accuracy, in plane accuracy, and inperformance as a reflecting surface.

Accordingly, by using as the submount 24, a material that can providehigh processing accuracy such as single-crystal silicon, it is possibleto obtain the taper mirror 8 having high accuracy without incurring arise in cost.

If the single-crystal silicon is used for the submount 24, the throughhole 7 is shaped in quadrangular pyramid. SiC, AlN and the like inaddition to Si can be used for the submount 24.

If the submount 24 is a non-conductive material, an electrode of a metalsuch as aluminum, not illustrated, is formed by deposition or the likeon the rear surface of the submount 24. That electrode is bonded to theelectrode (see the p-electrode 15 of FIG. 3) formed around thelight-emitting surface 6 of the light-emitting element 3 so thatelectric conductive relationship is established between the electrodes.Alternatively, the submount 24 may be bonded to the second substrate 25so that electric conductive relationship is established therebetween.

A difference between the submount 24 and the light-emitting element 3 inlinear expansivity is preferably set smaller than a difference betweenthe second substrate 25 and the light-emitting element 3 in linearexpansivity. Generally, a significant difference between the lead frame5 made of copper or the like and the light-emitting element 3 made ofGaAs or the like in linear expansivity can cause high thermal stress dueto a change in ambient temperature to make the light emission state ofthe light-emitting element 3 unstable. By selecting as the submount 24 amaterial less different from the light-emitting element 3 in linearexpansivity, thermal stress can be reduced, thereby ensuring a stableperformance in a wide temperature range. It is preferable to use, forexample, Si (linear expansivity: about 3 ppm/K) as the submount 24 ifcopper (linear expansivity: about 18 ppm/K) is used as the secondsubstrate 25 and GaAs (linear expansivity: 6 ppm/K) is used as thelight-emitting element 3. As described above, the use of Si alsofacilitates the processing of the through hole 7.

FIG. 17 shows an example of a rear surface side of the submount 24 (sideon which the light-emitting element is disposed). A gold-tin film 34 isformed by patterning around the outer periphery of the through hole 7.The gold-tin film 34 contains 20 to 30 wt % of tin with respect to gold.The p-electrode 15 (see FIGS. 2 and 3) of the light-emitting element 3,on the other hand, is formed of a thin film of gold. By positioning thethrough hole 7 with respect to the light-emitting surface 6 of thelight-emitting element 3, followed by heating while applying pressure,the gold-tin film 34 and the p-electrode 15 are forced to form aeutectic of gold and tin so that the light-emitting element 3 can bebonded to the submount 24. The light-emitting element 3 is indicated bythe dash lines in FIG. 17. A first electrode 35 is electricallyconnected to the gold-tin film 34, and also connected to the secondsubstrate 25 by the bonding wire 33. A second electrode 36, on the otherhand, is connected by the bonding wire 33 to the n-electrode 11 of thelight-emitting element 3 on its rear surface side, and also connected tothe second substrate 25 by the bonding wire 33. Thus, the light-emittingelement 3 is electrically connected via the submount 24 to the secondsubstrate 25.

In Embodiment 4, as in the case of Embodiment 1, the mold resin(light-transmissive resin member) may be provided on the front surfaceside of the second substrate 25 so as to be filled in the light-emissionhole 26 and in the through hole 7 and to have the lens formed as anintegral part of the mold resin. Alternatively, as in the case ofEmbodiment 2, the adhesive may be filled in the light-emission hole 26and in the through hole 7 to bond the lens so that the lens faces thelight-emission hole 26.

Embodiment 5

A yet another modification of the above optical transmitter according toEmbodiment 1 is given as an optical transmitter according to Embodiment5 and explained referring to FIG. 18. FIG. 18 is an explanatory viewshowing a schematic structure of the optical transmitter according toEmbodiment 5.

As shown in FIG. 18, in the optical transmitter 51 according toEmbodiment 5, the light-emitting element 3 is disposed on the submount24 so that the submount 24 is interposed between the light-emittingelement 3 and a third substrate 27. The submount 24 has a second throughhole 29 provided with a second mirror 32 as in the case of Embodiment 4.The third substrate 27 also has a first through hole 28 provided with afirst mirror 31 as in the case of Embodiment 1. The light-emittingelement 3 is positioned so that the light-emitting surface 6 faces thesecond through hole 29, and is disposed on the rear surface of thesubmount 24. The second through hole 29 of the submount 24 communicateswith the first through hole 28 of the third substrate 27.

Since both the first mirror 31 and the second mirror 32 are used, themirrors thickness is increased. As a result, the optical paths of lightbeams in an increased quantity can be changed, thereby increasing theoptical transmission efficiency. The first mirror 31 and the secondmirror 32 are preferably given different shapes in order to increase theoptical transmission efficiency and to allow the mirrors shape to bearbitrary selected depending on the radiation state of light beamsemitted from the light-emitting element 3.

Generally, a taper angle θ1 formed between the inner wall (first mirror31) of the third substrate 27 and the light-emitting surface 6 of thelight-emitting element 3 is preferably set greater than a taper angle θ2formed between the inner wall (second mirror 32) of the submount 24 andthe light-emitting surface 6 of the light-emitting element 3. This isbecause light beams from the light-emitting element 3 includes both alight beam having a wide radiation angle and a light beam having anarrow radiation angle, as shown in FIG. 22.

The second mirror 32, arranged closer to the light-emitting surface 6,receives a light beam having a wide radiation angle. Accordingly, thetaper angle θ2 of the second mirror 32 is set smaller. The first mirror31 receives a light beam with a narrow radiation angle. Accordingly, thetaper angle θ1 of the first mirror 31 is set greater. Thus, it isensured that the optical path of a light beam reflected from each mirroris changed substantially parallel to the optical axis of thelight-emitting element 3, thereby improving the efficiency of couplingwith the optical fiber.

Preferably the taper mirror of the first mirror 31 is set at 70° to 85°and the taper angle of the second mirror 32 is set at 40° to 70°. Thatis, since both the through hole of the third substrate 27 and thethrough hole of the submount 24 each have a mirror, the mirrorsthickness is increased so that the optical paths of light beams in abroader range of radiation angles can be changed and the mirrors anglecan be arbitrary selected depending on the radiation angles of lightbeams emitted from the light-emitting element 3, thereby achieving highutility efficiency.

Further, the use of the submount 24 produces the effect of reducingthermal stress created on the light-emitting element 3 as in the case ofEmbodiment 4. The submount 24 is preferably made of Si as in the case ofEmbodiment 4.

In Embodiment 5, as in the case of Embodiment 1, the mold resin(light-transmissive resin member) may be provided on the front surfaceside of the third substrate 27 so as to be filled in the first throughhole 28 and in the second through hole 29 and to have the lens formed asan integral part of the mold resin. Alternatively, as in the case ofEmbodiment 2, the adhesive may be filled in the first through hole 28and in the second through hole 29 to bond the lens so that the lensfaces the first through hole 28.

As has been described above, the optical transmitters 1, 21, 31, 41 and51 according to Embodiments 1 to 5 use either the through hole 7 formedin the lead frame 5 or in the submount 24, or the first through hole 28and the second through hole 29 formed in the third substrate 27 and inthe submount 24, respectively, in order to raise light beams radiatedfrom light-emitting element 3. Thus, the optical transmission efficiencyof these optical transmitters is increased and heat dissipation thereofis improved, while miniaturization and cost reduction of these opticaltransmitters can be achieved. The optical transmitters 1, 21, 31, 41 and51 according to Embodiments 1 to 5 are merely examples of the presentinvention and various modifications may be made without departing fromthe spirit of the invention.

Embodiment 6

An application of the above optical transmitter according to Embodiment1 is given as an optical transmitter according to Embodiment 6 andexplained referring to FIG. 19. FIG. 19 is an explanatory view showing aschematic structure of the illumination device according to Embodiment6.

As shown in FIG. 19, the illumination device 61 according to Embodiment6 of the present invention is the application of the above-describedoptical transmitter 1 according to Embodiment 1 (see FIG. 1).

In FIG. 19, light-emitting elements 3 a, 3 b and 3 c respectivelyradiate light beams having different wavelengths such as light beams inthree colors R, G and B (red, green and blue).

The optical path of a light beam radiated from each of thelight-emitting elements 3 a, 3 b and 3 c is changed by the taper mirror8 as described in Embodiment 1.

These light beams passes through the mold resin 9 to be applied onto alight scattering film 20 where the light beams in those colors arescattered and mixed together to become, for example, white color light,which is then emitted to the outside.

As described in Embodiment 1, since the lead frame 5 having the tapermirror 8 is used, a light beam which usually cannot be used because ofits wide radiation angle can be utilized effectively so that thelight-utilization efficiency can be increased.

Further, since heat dissipation is improved as mentioned above, theamount of electric current to pass through the light-emitting element 3can be increased. This makes it possible for the illumination device 61to have high luminance, to be miniaturized, and to be manufactured at alow cost. Depending on its usage, the illumination device 61 may includea plurality sets of light-emitting elements 3 a, 3 b and 3 c.

Embodiment 7

A modification of the above illumination device to Embodiment 7 is givenas an illumination device according to Embodiment 7 and explainedreferring to FIG. 20. FIG. 20 is an explanatory view showing a schematicstructure of the illumination device according to Embodiment 7 referringto FIG. 20.

As shown in FIG. 20, in the illumination device 71 according toEmbodiment 7, all the light-emitting elements 3 are adapted to radiatelight beams having the same wavelength such as light beams in bluecolor.

Light beams radiated from the light-emitting elements 3 enter a phosphor23 where part of the light beams is converted to light beams in yellowcolor or the like which are then mixed with the rest of the light beamsin original color to become light beams in white color or the like.

Alternatively, light beams in white color may be obtained by aconventionally known method, for example, by using the light-emittingelement 3 which emits ultraviolet light beam and causing the ultravioletlight beam to pass through phosphors 23 in R, G and B.

In Embodiment 7, the light-emitting element 3 is not an independent chipshown in FIG. 19 but has light-emitting surfaces 6 provided in array onthe same wafer.

The light-emitting surfaces 6 are arranged not only in a width directionshown in the figure but also in a depth direction, not illustrated. Thelight-emitting element 3 is provided with several tens to severalhundreds of light-emitting surfaces 6. This eliminates the need todispose independent chips. Consequently, the illumination device can bemanufactured at a low cost and miniaturized.

Also, in the light-emitting element 3, the electrodes (see then-electrode 11 of FIG. 3) are provided opposite the light-emittingsurfaces 6, respectively, and bonded to the rear-electrode substrate 22with the electrically conductive adhesive such as a silver paste.

The lead frame 5 and the rear-electrode substrate 22 are electricallyconnected to an electric circuit, not illustrated, for the on/offcontrol of the light-emitting element 3.

The rear-electrode substrate 22 is made of a metal having a high thermalconductivity such as aluminum, copper or phosphor bronze.

That is, the light-emitting element 3 is not electrically connected byan elongate member such as a wire. Instead, the electrode (see thep-electrode 15 of FIG. 3) of the light-emitting element 3 on thelight-emitting surface 6 side and the electrode thereof on the rearsurface side are in surface-to-surface contact with the lead frame 5 andthe rear-electrode substrate 22, respectively. Accordingly, heatgenerated at the light-emitting element 3 can be dissipated efficiently,so that heat dissipation can be significantly improved.

As has been described above, the illumination devices 61 and 71according to Embodiment 6 and Embodiment 7 use the through hole 7 formedin the lead frame 5 in order to raise light beams radiated from thelight-emitting element 3. Thus, the optical transmission efficiency ofthese optical transmitters is increased and heat dissipation thereof isimproved, while miniaturization and cost reduction of these opticaltransmitters can be achieved. The illumination devices 61 and 71according to Embodiment 6 and Embodiment 7 are merely examples of thepresent invention and various modifications may be made withoutdeparting from the spirit of the invention.

The illumination devices 61 and 71 according to the present inventioncan be applied extensively in backlights for liquid crystal device,luminaires for illuminator, headlights for automobile, and flashlightsfor camera, as well as general purpose luminaires.

INDUSTRIAL APPLICABILITY

The present invention provides the industrial applicability below.

(1) The substrate has the through hole. The through hole has the innerwall. The through hole has the inside diameter increasing from the rearsurface side of the substrate toward the front surface side thereof.Thus, of light beams radiated from the light-emitting portion, a lightbeam having a wide radiation angle can be reflected from the inner wallof the through hole toward the front surface of the substrate.Accordingly, a light beam having a wide radiation angle can be alsoeffectively utilized for optical coupling with an optical fiber or thelike, increasing the coupling efficiency.

(2) The light-emitting element is disposed on the rear surface of thesubstrate so that the light-emitting portion is exposed within thethrough hole. Thus, the light-emitting portion of the light-emittingelement is close to the inner wall of the through hole. Accordingly, itis possible to reduce to a minimum the depth of the through holeinvolved in reflection of a light beam having a wide radiation angletoward the front surface of the substrate. Consequently, miniaturizationof the optical transmitter can be achieved.

(3) The through hole formed in the substrate serves as a guide for lightbeams radiated from the light-emitting element. Thus, the substrateoriginally for use as a wiring component can also be utilized as anoptical component. Accordingly, the number of components can be reducedand the production process can be simplified. Consequently, the opticaltransmitter can be manufactured at a low cost.

(4) The light-emitting element disposed so that the light-emittingportion is exposed within the through hole. Thus, the light-emittingportion as a heat-generating source is close to the substrate as aheat-dissipating medium. Accordingly, heat dissipation of thelight-emitting element is improved.

(5) The light-emitting element and the bonding wire can be encapsulatedin the mold resin containing the filler. Thus, thermal stress created onthe light-emitting element and on the bonding wire can be reduced.Further, the light-emitting surface of the light-emitting element can becovered with the resin having resiliency. The light-emitting element canbe disposed on the submount having a linear expansivity similar to thatof the light-emitting element. Accordingly, thermal stress created onthe light-emitting element can be reduced, so that the opticaltransmitter can be used and stored over a wide temperature range to gaina high reliability.

1. An optical transmitter comprising: a substrate having a through hole;and a light-emitting element disposed on a rear surface of the substrateand having a light-emitting portion, the through hole having an innerwall, the through hole having an inside diameter increasing from a rearsurface side of the substrate toward a front surface side thereof, thelight-emitting element disposed so that the light-emitting portion isexposed within the through hole, the light-emitting portion radiatinglight beams toward a front surface of the substrate, the through holebeing such that part of the light beams goes out the through holewithout being reflected, and that the other light beams go out thethrough hole after being reflected from the inner wall thereof.
 2. Theoptical transmitter of claim 1, wherein the substrate is a lead framefor providing a connection to an outside electric circuit.
 3. Theoptical transmitter of claim 1, wherein the light-emitting elementincludes an electrode provided around the light-emitting portion, theelectrode electrically connected to the rear surface of the substrate.4. The optical transmitter of claim 1, wherein the through holecomprises a first inner-wall portion provided on the rear surface sideof the substrate and a second inner-wall portion provided on the frontsurface side of the substrate, the first inner-wall portion having aninside diameter gradually increasing toward the front surface side ofthe substrate, the second inner-wall portion having an inside diametergreater than a maximum inside-diameter of the first inner-wall portion.5. The optical transmitter of claim 1, wherein the inner wall of thethrough hole is concavely curved.
 6. The optical transmitter of claim 1,wherein the substrate has a thickness of 50 to 500 μm.
 7. The opticaltransmitter of claim 1, further comprising an auxiliary substratearranged so that the light-emitting element is sandwiched between theauxiliary substrate and the substrate, the light-emitting element havinga rear electrode on a rear surface thereof opposite the light-emittingportion, the rear electrode electrically connected to the auxiliarysubstrate.
 8. The optical transmitter of claim 1, further comprising anencapsulating resin-member provided on the rear surface side of thesubstrate for encapsulating the light-emitting element.
 9. The opticaltransmitter of claim 8, wherein the encapsulating resin-member is madeof a resin, the resin containing a filler for lowering a linearexpansivity of the encapsulating resin-member and for raising a thermalconductivity thereof.
 10. The optical transmitter of claim 1, furthercomprising a transparent resin filled in the through hole and coveringthe light-emitting surface of the light-emitting element.
 11. Theoptical transmitter of claim 10, further comprising a lens bonded by thetransparent resin filled in the through hole so that the lens faces thethrough hole of the substrate.
 12. The optical transmitter of claim 10,wherein the transparent resin has a hardness of 50 degrees or loweraccording to JIS-A.
 13. The optical transmitter of claim 1, furthercomprising a light-transmissive resin member provided on the frontsurface side of the substrate so as to be filled in the through hole,the light-transmissive resin member having a lens formed as a partthereof for collecting light beams radiated from the light-emittingelement.
 14. The optical transmitter of claim 13, wherein the substratehas a resin-injection groove formed in the front surface thereof, theresin-injection groove communicating with the through hole forfacilitating the flow of a light-transmissive resin into the throughhole at the formation of the light-transmissive resin member.
 15. Anoptical transmitter comprising: a substrate having an opening; asubmount attached to the substrate and having a through hole; and alight-emitting element disposed on a rear surface of the submount andhaving a light-emitting portion, the through hole having an inner wall,the through hole having an inside diameter increasing from a rearsurface side of the submount toward a front surface side thereof, thelight-emitting element disposed so that the light-emitting portion isexposed within the through hole, the light-emitting portion radiatinglight beams toward the opening of the substrate, the through hole beingsuch that part of the light beams goes out the through hole and entersthe opening of the substrate without being reflected, and that the otherlight beams goes out the through hole into the opening of the substrateafter being reflected from the inner wall thereof.
 16. The opticaltransmitter of claim 15, wherein a difference in linear expansivitybetween the submount and the light-emitting element is set smaller thana difference in linear expansivity between the substrate and thelight-emitting element.
 17. The optical transmitter of claim 15, whereinthe submount is made of silicon, the silicon anisotropically etched toform the through hole.
 18. The optical transmitter of claim 15, whereinthe substrate is a lead frame for providing a connection to an outsideelectric circuit.
 19. The optical transmitter of claim 15, thelight-emitting element includes an electrode provided around thelight-emitting portion, the electrode electrically connected to the rearsurface of the submount.
 20. The optical transmitter of claim 15,wherein the through hole comprises a first inner-wall portion providedon the rear surface side of the submount and a second inner-wall portionprovided on the front surface side of the submount, the first inner-wallportion having an inside diameter gradually increasing toward the frontsurface side of the submount, the second inner-wall portion having aninside diameter greater than a maximum inside-diameter of the firstinner-wall portion.
 21. The optical transmitter of claim 15, wherein theinner wall of the through hole is concavely curved.
 22. The opticaltransmitter of claim 15, wherein the submount has a thickness of 50 to500 μm.
 23. The optical transmitter of claim 15, further comprising anauxiliary substrate arranged so that the light-emitting element issandwiched between the auxiliary substrate and the submount, thelight-emitting element having a rear electrode on a rear surface thereofopposite the light-emitting portion, the rear electrode electricallyconnected to the auxiliary substrate.
 24. The optical transmitter ofclaim 15, further comprising an encapsulating resin-member provided on arear surface side of the substrate for encapsulating the submount andthe light-emitting element.
 25. The optical transmitter of claim 24,wherein the encapsulating resin-member is made of a resin, the resincontaining a filler for lowering a linear expansivity of theencapsulating resin-member and for raising a thermal conductivitythereof.
 26. The optical transmitter of claim 15, further comprising atransparent resin filled in the through hole and in the opening andcovering the light-emitting surface of the light-emitting element. 27.The optical transmitter of claim 26, further comprising a lens bonded bythe transparent resin filled in the through hole and in the opening sothat the lens faces the opening of the substrate.
 28. The opticaltransmitter of claim 26, wherein the transparent resin has a hardness of50 degrees or lower according to JIS-A.
 29. The optical transmitter ofclaim 15, further comprising a light-transmissive resin member providedon a front surface side of the substrate so as to be filled in thethrough hole and in the opening, the light-transmissive resin memberhaving a lens formed as a part thereof for collecting light beamsradiated from the light-emitting element.
 30. The optical transmitter ofclaim 29, wherein the substrate has a resin-injection groove formed inthe front surface thereof, the resin-injection groove communicating withthe opening for facilitating the flow of a light-transmissive resin intothe opening and into the through hole communicating therewith at theformation of the light-transmissive resin member.
 31. An opticaltransmitter comprising: a substrate having a first through hole; asubmount attached to the substrate and having a second through hole; anda light-emitting element disposed on a rear surface of the submount andhaving a light-emitting portion, the first through hole having an innerwall, the first through hole having an inside diameter increasing from arear surface side of the substrate toward a front surface side thereof,the second through hole having an inner wall, the second through holehaving an inside diameter increasing from a rear surface side of themount toward a front surface side thereof, the light-emitting elementdisposed so that the light-emitting portion is exposed within the secondthrough hole, the light-emitting portion radiating light beams toward afront surface of the substrate, the first through hole and the secondthrough hole being such that part of the light beams goes out the firstthrough hole without being reflected, and that the other light beams goout the first through hole after being reflected from at least one ofthe inner wall of the substrate and the inner wall of the submount. 32.The optical transmitter of claim 31, wherein a difference in linearexpansivity between the submount and the light-emitting element is setsmaller than a difference in linear expansivity between the substrateand the light-emitting element.
 33. The optical transmitter of claim 31,wherein an angle formed between the inner wall of the first through holeand an optical axis of the light-emitting element is set smaller than anangle formed between the inner wall of the second through hole and theoptical axis of the light-emitting element.
 34. The optical transmitterof claim 31, wherein the submount is made of silicon, the siliconanisotropically etched to form the through hole.
 35. The opticaltransmitter of claim 31, wherein the light-emitting element includes anelectrode provided around the light-emitting portion, the electrodeelectrically connected to the rear surface of the submount.
 36. Theoptical transmitter of claim 31, wherein the substrate is a lead framefor providing a connection to an outside electric circuit.
 37. Theoptical transmitter of claim 31, wherein the first through holecomprises a first inner-wall portion provided on the rear surface sideof the substrate and a second inner-wall portion provided on the frontsurface side of the substrate, the first inner-wall portion having aninside diameter gradually increasing toward the front surface side ofthe substrate, the second inner-wall portion having an inside diametergreater than a maximum inside-diameter of the first inner-wall portion.38. The optical transmitter of claim 31, wherein the second through holecomprises a first inner-wall portion provided on the rear surface sideof the submount and a second inner-wall portion provided on the frontsurface side of the submount, the first inner-wall portion having aninside diameter gradually increasing toward the front surface side ofthe submount, the second inner-wall portion having an inside diametergreater than a maximum inside-diameter of the first inner-wall portion.39. The optical transmitter of claim 31, wherein the inner wall ofeither the first through hole or the second through hole is concavelycurved.
 40. The optical transmitter of claim 31, wherein the substrateand the submount each have a thickness of 50 to 500 μm.
 41. The opticaltransmitter of claim 31, further comprising an auxiliary substratearranged so that the light-emitting element is sandwiched between theauxiliary substrate and the submount, the light-emitting element havinga rear electrode on a rear surface thereof opposite the light-emittingportion, the rear electrode electrically connected to the auxiliarysubstrate.
 42. The optical transmitter of claim 31, further comprisingan encapsulating resin-member provided on the rear surface side of thesubstrate for encapsulating the submount and the light-emitting element.43. The optical transmitter of claim 42, wherein the encapsulatingresin-member is made of a resin, the resin containing a filler forlowering a linear expansivity of the encapsulating resin-member and forraising a thermal conductivity thereof.
 44. The optical transmitter ofclaim 31, further comprising a transparent resin filled in the firstthrough hole and in the second through hole and covering thelight-emitting surface of the light-emitting element.
 45. The opticaltransmitter of claim 44, further comprising a lens bonded by thetransparent resin filled in the first through hole and in the secondthrough hole so that the lens faces the first through hole of thesubstrate.
 46. The optical transmitter of claim 44, wherein thetransparent resin has a hardness of 50 degrees or lower according toJIS-A.
 47. The optical transmitter of claim 31, further comprising alight-transmissive resin member provided on a front surface side of thesubstrate so as to be filled in the first through hole and in the secondthrough hole, the light-transmissive resin member having a lens formedas a part thereof for collecting light beams radiated from thelight-emitting element.
 48. The optical transmitter of claim 47, whereinthe substrate has a resin-injection groove formed in the front surfacethereof, the resin-injection groove communicating with the first throughhole for facilitating the flow of a light-transmissive resin into thefirst through hole and into the second through hole communicatingtherewith at the formation of the light-transmissive resin member.